Chapter 7: The Sensory Systems Lesson 7.2 The Ear

The Ear A. Anatomy of the ear B. Functions of the ear External Ear (Outer) Middle Ear (Tympanic Cavity) Internal Ear (Inner) B. Functions of the ear 1. Hearing 2. Equilibrium (balance) C. Disorders and infections of the ear 1. Deafness 2. Tinnitus 3. External Otis 4. Otitis Media 5. Labyrinthitis

Anatomy of the Ear External ear Auricle (pinna) channels sound waves in many animals not very helpful in humans Auditory canal (external acoustic meatus) Short tube, one inch long, ¼ inch in diameter Walls of the canal are lined with skin cells with Ceruminous glands = secrete cerumen (earwax) Earwax – cleans, lubricates, and protects Tympanic membrane (Ear drum) Separates outer ear from middle ear Membrane vibrates when sound waves strike it

Anatomy of the Ear Middle ear (Tympanic Cavity) Small open chamber in temporal lobe of skull Oval Window is a membrane covered opening Ossicles (smallest bones in human body) They connect tympanic membrane to oval window Transmit AND amplify sound waves Hammer = maleus Anvil = incus Stirrup = stapes Eustachian tube Connects the middle ear to the pharynx Serves to equalize the pressure on either side of the tympanic membrane

Anatomy of the Ear Internal ear (inner ear) Cochlea – Snail like structure used for hearing Vestibulocochlear nerve – carries information to brain Cochlear nerve (hearing information) Vestibular nerve (balance information) Vestibule & Semicircular canals Used in coordination of balance. Semicircular canals (Bony labyrinth) filled with: Clear fluid (perilymph) Membrane covered tubes (membranous labyrinth) Inside tubes is thicker fluid (endolymph)

Anatomy of the Ear

Functions of the Ear Hearing - Sound waves enter the auditory canal & cause tympanic membrane to vibrate - This vibration stimulates the ossicles to transmit and amplify vibrations to the oval window. - The oval window vibrations are passed to the cochlea - Cochlea - cochlear duct (membranous labyrinth) filled with the Organ of Corti – contains receptor hairs - As the fluid in the cochlea vibrates, the receptor hairs are stimulated: - short stiff hairs stimulated by high pitch sounds - long flexible hairs by low pitch sounds - Receptor hairs transmit signals through the vestibulocochlear nerve to the brain

Functions of the Ear Equilibrium (balance) Vestibule contains three semicircular canals Tiny receptor hairs in the semicircular canals are stimulated by the moving endolymph The receptor hairs stimulate the vestibular nerve and transmit information to the cerebellum Information about the position of the head, orientation and motion are also sent.

Disorders and Infections of the Ear Deafness – term for any loss of hearing Many causes: damage to hair receptors, excessive earwax, scaring on the tympanic membrane, etc.. Presbycusis = age related hearing loss In-canal hearing aid, half shell, behind the ear Tinnitus – “ringing in the ear” Caused by damaged hair cells (move randomly) from repeat sounds External otitis (swimmer’s ear) = fungal infection of auditory canal Otitis media (middle ear infection) = bacterial/viral infection Associated with upper respiratory infections in infants (tubes to drain) Labyrinthitis (inner ear infection) swelling disrupts semicircular canals Causes Vertigo (dizziness), chronic = Meniere disease